The invention broadly relates to tools for use in completion or reworking fluid-bearing wells, and, more particularly to a tool assembly, connected to the downhole end of a dry tubing string, which is drop bar actuated to provide an instantaneous full opening into the tubing, surging fluids and particulate matter inwardly from the formation and upwardly into the tubing.
When sinking boreholes as source wells into rock strata having reservoirs of the desired fluids by the rotary drilling method, the commonly utilized liquid mixture, or drilling "mud", imparts fluid and solid losses into the rock reservoir matrix. While these losses may be relatively controlled, some degree of contamination and alteration is inherent in the drilling procedure, resulting in formation damage which limits productivity. When casing is cemented through the pay zone, additional damage occurs from losses of cement filtrate and whole cement. Although openhole completions and isolation tools can prevent cement contamination, the more common method of cementing casing across the zone of interest necessarily leads to contamination. Still other damage is produced by the mechanics of perforating through the casing necessary to open the pay zone. The tightly compacted linings of the perforation tunnels and shot debris restrict production inflow. Limited or unsuccessful penetration of the casing, cement sheath, and damage zone by the perforations add to the damage factor.
It is to the removal of formation damage through the means of a controlled and instantaneous release of the maximum differential pressure available that the present invention is primarily addressed.
Utilization of differential pressure techniques, per se, for mechanical advantage in well completion operations is known in the prior patented art. Swabbing is an early art form in which hydrostatic pressure is slowly relieved from the open reservoir. However, damage is not frequently removed by swabbing. Frangible discs, pressure relief valves, and recoverable plugs have been offered to accomplish limited tests and backsurging for damage removal in well completions. The prior art also reveals plugs of the knock-out variety which are activated by a weight dropped through the tubing string. Robert D. Yeates, U.S. Pat. No. 4,182,419 discloses such a plug, while Robert D. Yeates, U.S. Pat. No. 4,211,280 teaches a related method of completing a well. U.S. Pat. No. 4,151,881 to Armstrong also discloses a plug which is drop bar actuated to provide communication between the borehole and a dry tubing string. Another tubing bottom plug of this general type, which is run through tubing and utilized for related surging operations, is shown in U.S. Pat. No. 4,142,583 to Brieger. The present invention is an advancement over this previous art.